This study compared functional and physiologic measures of ambulation and upright mobility with functional electrical stimulation (FES) versus knee-ankle-foot-orthoses (KAFO) in an 11-year-old boy with a T-10 level spinal cord injury. The child was a limited community ambulator with bilateral KAFO and loftstrand crutches. The FES system consisted of percutaneous intramuscular electrodes controlled by a portable stimulator and thumbswitch, an AFO for ankle and foot support, and loftstrand crutches. The subject used a swing-through gait pattern with both modes of mobility. The Functional Independence Measure scoring system and time to completion were used to compare performance in 6 standardized activities: donning, high transfer, inaccessible toilet transfer, ascend/descend stairs, and floor-to-standing transfer. Ten repeated measures were performed for each mode. Physiologic measures included energy expenditure, postural stability using forceplates, and a Functional Standing Test (FST). The subject performed all 6 mobility activities independently with FES and KAFO. In 4 of 6 activities, there was a trend toward faster times with FES, but this was not statistically significant. Toilet transfers and stair descent were performed significantly faster with KAFO. There was no difference in completion times on the activities of the FST. Measures of postural sway suggested that the subject was more stable with KAFO during quiet standing, while the modes were equal during a dynamic activity (raising arm for functional use). Energy expenditure results revealed no significant difference in oxygen cost per meter but a significantly higher oxygen consumption rate per minute for FES. Ambulation with both modes was performed at levels consistent with strenuous exercise. Maximum ambulation distances were relatively equal while the subject's velocity was significantly faster with FES. Of note, the subject reported ceasing ambulation during maximum distance trials due to general fatigue when using FES and due to shoulder pain with KAFO ambulation. For this subject, FES provided a means of performing upright mobility tasks independently, comparable with that of KAFO, while providing a faster ambulation velocity and a potential means of cardiovascular training.